In our previous chapter, we started writing data into our Kafka system. However, as you know, that is only one part of the story. Consumers get the data from Kafka and provide those values to other systems or applications. Because consumers are clients that exist outside of brokers, they can be written in various programming languages just like producer clients. Take note that when we look at how things work in this chapter, we will try to lean towards the defaults of the Java consumer client. After reading this chapter, we will be on our way to solving our previous business requirements by consuming data in a couple of different ways.
The consumer client is the program that subscribes to the topic or topics that interest them [1]. As with producer clients, the actual consumer processes can run on separate machines and are not required to run on a specific server. In fact, most consumer clients in production settings are on separate hosts. As long as the clients can connect to the Kafka brokers, they can read messages. Figure 5.1 reintroduces the broad scope of Kafka and shows consumers running outside the brokers to get data from Kafka.
